Contact-free operating electronic switchgear

Abstract

A contact-free operating electronic switchgear, having an oscillator capable of being externally affected, a switching amplifier with at least two operating units disposed downstream of the oscillator, an electronic switch, which can be controlled by the oscillator via the switching amplifier, and a supply circuit for the provision of the supply voltage for the oscillator and for the switching amplifier, is shown and described. In electronic switchgear operating contact-free in accordance with the invention the maximum switching frequency is considerably increased in that a control circuit is provided between the two operating units of the switching amplifier and the oscillator and that the oscillator is controlled by means of the control circuit in such a way that the oscillator also oscillates in the affected state.

I claim: 
     
       1. A contact-free operating electronic switchgear, comprising an oscillator capable of being externally affected, a switching amplifier having at least two operating units disposed downstream of the oscillator, an electronic switch which can be controlled by the oscillator via the switching amplifier, a supply circuit for the provision of a supply voltage for the oscillator and for the switching amplifier, and a control circuit between the two operating units of the switching amplifier and the oscillator, wherein the control circuit controls the oscillator such that the oscillator also oscillates when it is externally affected. 
     
     
       2. An electronic switchgear in accordance with claim 1, wherein the first operating unit of the switching amplifier comprises a demodulator. 
     
     
       3. An electronic switchgear in accordance with claim 2, wherein the demodulator comprises a reference voltage source, a differential amplifier and a demodulator condenser connected directly or indirectly to a signal output of the differential amplifier. 
     
     
       4. An electronic switchgear in accordance with claim 3, wherein the demodulator further comprises a switching transistor, a load resistor and a constant current network and the demodulator condenser is charged with a constant charge current via the constant current network and is discharged with a constant charge current. 
     
     
       5. An electronic switchgear in accordance with claim 3, further comprising a constant charge-current generator and a constant discharge current generator connected to a signal output of the differential amplifier and the demodulator condenser is charged with a constant charge current from the constant charge-current generator and is discharged with a constant discharge current from the constant discharge-current generator. 
     
     
       6. An electronic switchgear in accordance with claim 4, wherein the constant charge current is greater, preferably by a factor of 2 to 3, than the constant discharge current. 
     
     
       7. An electronic switchgear in accordance with claim 5, wherein the constant charge current is greater, preferably by a factor of 2 to 3, than the constant discharge current. 
     
     
       8. An electronic switchgear in accordance with claim 3, wherein the second operating unit of the switching amplifier comprises a Schmitt trigger. 
     
     
       9. An electronic switchgear in accordance with claim 8, wherein the Schmitt trigger has two comparison inputs, a control input and a signal output and the control output of the Schmitt trigger is connected with the demodulation condenser. 
     
     
       10. An electronic switchgear in accordance with claim 9, further comprising a voltage divider connected to the supply voltage and having three voltage divider resistors and two connecting points, one of said connecting points being located near a positive terminal of the supply voltage and the other of said connecting points being located near a negative terminal of the supply voltage, and one comparison input of the Schmitt trigger is connected to the connecting point of the voltage divider resistors located near a positive terminal of the supply voltage and the other comparison input of the Schmitt trigger is connected to the connecting point of the voltage divider resistors located near a negative terminal of the supply voltage. 
     
     
       11. An electronic switchgear in accordance with claim 3, wherein the control circuit comprises an analog amplifier with a reference input, a control input and a control output and wherein the reference input is connected to a reference voltage, the control input is connected to the demodulator condenser and the control output is connected to the oscillator. 
     
     
       12. An electronic switchgear in accordance with claim 10, wherein the voltage divider has a fourth voltage divider resistor and a further connecting point between the third voltage divider resistor and the fourth voltage divider resistor said voltage divider being connected via the fourth voltage divider resistor to the negative terminal of the supply voltage and wherein the reference input of the analog amplifier of the control circuit is connected to the connecting point between the third voltage diver resistor and the fourth voltage divider resistor. 
     
     
       13. An electronic switchgear in accordance with claim 11, wherein the oscillator has an oscillator transistor with an emitter resistor, and be means of the control circuit a control resistor can be switched in parallel with the emitter resistor of the oscillator transistor. 
     
     
       14. An electronic switchgear in accordance with claim 13, wherein the control circuit has a control transistor with a collector emitter path, the base of the control transistor is connected to the control output of the analog amplifier and wherein the control resistor can be switched in parallel with the emitter resistor of the oscillator transistor by means of the collector emitter path of the control transistor. 
     
     
       15. An electronic switchgear in accordance with claim 13, further comprising a hysteresis resistor and a hysteresis transistor with a collector emitter path, the hysteresis resistor being in series with the emitter resistor of the oscillator transistor, the base of the hysteresis transistor being connected to the signal output of the Schmitt trigger and the collector emitter path of the hysteresis transistor is connected parallel to the hysteresis resistor. 
     
     
       16. An electronic switchgear in accordance with claim 9, further comprising a hysteresis resistor and an hysteresis transistor with a collector emitter path, the hysteresis resistor being in series with the emitter resistor of the oscillator transistor, the base of the hysteresis transistor being connected to the signal output of the Schmitt trigger and the collector emitter path of the hysteresis transistor is connected parallel to the hysteresis resistor.